Mental health billing has a range of cpt codes from 90801-90853 and the diagnoses range from 296.** - 303.**. But it is very similar to regular billing. Substance abuse is mental health but in NY state it must be in an OASAS facility. If it is a facility then the billing is different (usually done on a UB04 form).
If you are billing for a couple and the diagnosis is marital problems, you bill under one of the patients, and use the code for family therapy with patient present and a diagnosis of marital problems. Most insurances do not cover it. However, if you are billing for a couple but the diagnosis is something other than marital problems then you would bill under the one that the diagnosis applies to and again bill as family therapy.
Michele